How to send my Lenovo Tablet to be repaired? (UK)?

I suspect my Lenovo tablet screen to be broken. Not the glass on top but underneath because it is not showing anything except a crack and lines from top to bottom.
I checked whether it was still under warranty and it still is (190 days left) but I don't know where to start for it to be sent off and repaired. Could someone maybe guide me on this please?

Thanks

PS If you haven't gathered I'm from the UK, so it would be preferably to have a UK based website.